Capacitive information disc playback styli are generally fabricated from hard dielectric materials such as diamond, sapphire, and the like. In order to reduce cost the dielectric material is mounted in a shank rather than employing a relatively large block of the dielectric material. The shank may be a metal such as titanium or any other suitable material.
Diamond is a preferred dielectric material because of its long wearing properties. In order to reduce cost either a synthetic or a natural diamond mounted in a shank may be employed. Diamond, like other dielectric materials, has an anisotropic hardness which depends on the crystallographic direction.
The diamonds as well as the other dielectric materials often have various crystalline faces which are undesirable for producing uniform video disc playback styli. One method for producing uniform styli is to form a cone at the tip of the dielectric material opposite the shank. The cone end is then shaped so that a disc engaging terminal portion is formed which can be employed to recover information from the capacitive information disc.
A problem caused by coning is the loss of the crystalline faces which provide a means for orienting the dielectric material and determining whether it is properly aligned--that is, the crystallographic axis has the desired relationship to the shank axis.